At this time, we're investigating the problem and looking for a solution.
If you've encountered this issue while converting your file, we suggest attempting to create and upload an EPUB directly to our system.
While there are a number of EPUB conversion options, Calibre (Download Here) has shown the best results for creating an EPUB for the Lulu system. Please review their extensive Help resources (Found Here) to create an EPUB 2 that our system can validate.
We've also created this Forum Thread. Post questions here and we'll do our best to respond and assist.
Question on custom ISBNs and eBook formats
I already have my own ISBNs and I'm looking to publish in ebook format and sell to multiple outlets. But I'm confused on one point. How is it possible that a Lulu project with a single ISBN can be distributed to channels that can't (or shouldn't) reuse the same ISBN?
From the video tutorials I've seen, it looks like for a new project I can: 1) provide my own ISBN, and then 2) distribute to different outlines (for example, EPUB edition for iBooks and MOBI for Kindle). But I don't get how that can work.